1) Field of the Invention
This invention relates generally to fabrication of metal lines for semiconductor devices and more particularly to the fabrication of a Al-Cu and TiN stack and more particularly to a sputter process to from Ti-rich TiN and TIN and Al layers.
2) Description of the Prior Art
Integrated circuits are formed upon semiconductor substrates within and upon whose surfaces are formed resistors, transistors, diodes and other electrical circuit elements. The electrical circuit elements are connected internally and externally to the substrate and to each other. It is common to use Al lines to interconnect these devices.
A problem with Al lines is electromigration (EM). EM is the transport of metal ions through a conductor and it results from the passage of direct electrical current. The reliability of a metal interconnect is more commonly described by a lifetime experiment on a set of lines to obtain the median time to failure (MFT). The stress experiment involves stressing the lines with high current densities at high temperatures. The failure criterion is typically an electrical open for nonbarrier conductors or about a 20% increase in line resistance for barrier metalization.
There is a challenge to form Al metal lines that have a high EM resistance using simpler processes.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patents and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following: U.S. Pat. No. 5,759,916(Hsu et al.) shows a Ti-rich TiN layer/TIN/AlCu layer. U.S. Pat. No. 5,462,895(Chen) and U.S. Pat. No. 5,525,543(Chen) show Ti-rich TiN/TiN barrier layers formed by CVD. U.S. Pat. No. 5,604,155 (Wang) teaches a Ti/TiN/Ti barrier layer. U.S. Pat. No. 5,756,396(Lee et al.) shows a TiN barrier layer.
However, better, simpler processes must be developed to form Al metal lines that have higher EM resistance.